Authentication and security in wireless communication system

ABSTRACT

A communication system having a wireless trunk for connecting multiple phone lines over wireless communication links to a cellular network comprises a central telephone switch, such as a private branch exchange or key system, connected through one or more trunk lines to a wireless access communication unit. The wireless access communication unit preferably comprises a separate subscriber interface for each trunk line from the central telephone switch. The wireless access communication unit collects data from each of the subscriber interfaces, formats the data into a format compatible with an over-the-air protocol, and transmits the information over one or more wireless channels to a cellular base station. The wireless access communication unit thereby connects calls received from the central telephone switch&#39;s trunk lines over a wireless trunk to a network. A controller within the wireless access communication unit interfaces the subscriber interfaces with a radio transceiver, and assists in the conversion of data from a format suitable for wireless transmission. Authentication is carried out separately for each of the subscriber interfaces, thereby allowing the wireless access communication unit to represent itself as multiple individual subscribers to the network. Upon each initial registration, each subscriber interface derives its own ciphering key from a stored user key and uses it thereafter for encryption and decryption.

CROSS REFERENCE TO RELATED APPLICATIONS

This continuation application claims the benefit of U.S. patentapplication Ser. No. 08/988,505 for Authentication and Security inWireless Communications System, to inventors Bilgic and Menon, AssigneeIntel Corporation, filed Dec. 10, 1997 now U.S. Pat. No. 6,580,906.

BACKGROUND OF THE INVENTION

1) Field of the Invention

The field of the present invention relates to a method and system forproviding communication services, and more particularly to techniquesfor authentication and security in a wireless communication system.

2) Background

Localized telephone switching systems such as private branch exchanges(PBXs) and key type systems have for many years been available tobusiness offices and other establisliments as an alternative or adjunctto public telephone service. A PBX or key system allows users connectedto the system to place intra-system telephone calls without accessingthe public telephone service. Such a system can provide significanteconomic benefits, particularly if intra-system telephone traffic isheavy.

On the other hand, when callers using a PBX or key system need to placea call to a party not connected to the system, such outside calls musttypically be routed through the PBX or key system controller overlandlines to the public telephone company. To accommodate such dualfunctionality (i.e., intra-system call support and outside callsupport), special-purpose telephones have been developed for connectionto a PBX or key system to allow manual routing of telephone calls. Forexample, deskset telephones can be provided with buttons correspondingto different telephone lines. By depressing the appropriate button, theuser selects between certain designated lines for calls within thesystem, or different designated lines for calls over the publictelephone network.

In other PBX and key systems call routing over the selected lines may beautomatic. For example, the user may select an intra-system call or acall over the public telephone network according to the first digitdialed, and the PBX or key system then analyzes the first digit androutes the call to the proper destination using the appropriate vehicle.

While PBX and key systems are useful for providing economical coveragewithin a private local telephone system, for long distance the PBX usersor key system users may still be required to rely on a local exchangecarrier (LEC) whose landlines are connected to the PBX. The localexchange carrier then routes the call to along distance carrier. Becausethe user must pay both the local exchange carrier and long distancecarrier for each long distance telephone call, long distance telephoneservice can be quite costly, particularly if the volume of long distancecalls is large.

Besides high costs for long distance service, another potentialdisadvantage of existing PBX or key telephone systems is that deploymentcan be difficult or expensive in remote areas. For example, if longdistance service or other public network services are required, thendeployment of a PBX or key system is generally limited to wherelandlines have been laid, so that the PBX or key system can have aconnection to a local exchange carrier which connects to the longdistance provider. If no landlines are present in the desired deploymentlocation, then it can be expensive to connect landlines to provide longdistance access for the PBX or key system. Also, conventional PBX or keysystems are generally not very mobile where they require an interfacewith landlines for long distance access or other types of public networkservices.

There is a need for a communication system having the ability of a PBXor key telephone system to manage local area calls, yet also which canprovide access to lower cost, reliable long distance or other networkservices. There is also a need for a versatile mechanism for allowingPBX or key type systems to achieve relatively inexpensive access tonetwork resources and long distance coverage. There is also a need for acommunication system that employs a robust, flexible protocol forproviding long distance coverage or other network services to localusers of a PBX, key system or other type of local area network.

SUMMARY OF THE INVENTION

The invention provides in one aspect a communication system having awireless trunk for connecting multiple phone lines over wirelesscommunication links to a cellular network. In one embodiment of theinvention, a central telephone switch or customer premises equipment(CPE), such as a private branch exchange or key system, is connectedthrough one or more trunks to a wireless access communication unit. Thewireless access communication unit provides the CPE with one or morewireless communication channels to a cellular network. Calls may beselectively routed by the CPE over landlines to a network or, instead,to the wireless access communication unit, thereby bypassing landlines.Multiple wireless access communication units in a geographical regioncan communicate with a single base station of the cellular network, solong as the base station capacity and current traffic load permit.

In another aspect of the invention, a wireless access communication unitis provided which has multiple trunk interfaces for connection to a CPE,and a radio transceiver for establishing one or more wirelesscommunication links to a cellular network. Each trunk interface isconnected to a line card comprising a vocoder and a subscriberinterface. A controller interfaces the line cards with the radiotransceiver, and assists in the conversion of data from a formatsuitable for wireless transmission to a format suitable for transmissionover the CPE trunk, and vice versa. Data communicated between thewireless access communication unit and the network may be encrypted atthe wireless access communication unit and decrypted at the mobileswitching center or else at a separate transcoding unit interposedbetween the mobile switching center and the base station subsystem.

In another aspect of the invention, each trunk interface of a wirelessaccess communication unit is individually authenticated and derives anindividual and unique ciphering key for encryption and decryption ofdata. A user key is stored at each trunk interface and at a centralregister of the network. During an authentication procedure, anauthentication parameter (e.g., a random number) is transferred to thetrunk interface, which generates a signed response and a ciphering keybased upon the stored user key. The network generates a matching signedresponse and ciphering key at its end. The wireless access communicationunit transmits the signed response back to the network, where it isverified before further communication is allowed to proceed.

In a preferred embodiment of the invention, the wireless accesscommunication unit operates according to a protocol utilizing aspects offrequency division multiple access (FDMA), time division multiple access(TDMA) and/or code division multiple access (CDMA), wherebycommunication channels are assigned to the wireless communication uniton a demand basis. In a preferred embodiment, communication between thewireless access communication unit and a base station of the cellularnetwork is carried out over a plurality of wireless duplex communicationchannels, one channel for each CPE trunk, with base transmissions intime slots on one frequency band and user transmissions (including thosefrom the wireless access communication unit) in time slots on adifferent frequency band. In such an embodiment, the user time slots maybe offset in time from the base time slots, and radio transmissions maybe carried out using spread spectrum techniques.

In another aspect of the invention, the wireless access communicationunit registers each CPE trunk to which it is connected such that eachCPE trunk appears as a subscriber to the network. Each CPE trunk maytherefore be addressed by a unique subscriber identifier. The wirelessaccess communication unit preferably utilizes aspects of GSM signalingto communicate information to the network, such that communication witha GSM-based network is carried out transparently by the wireless accesscommunication unit.

In yet another aspect of the invention, the wireless accesscommunication unit periodically re-registers each of its CPE trunks. Thebase station receives and monitors the re-registration signals from thewireless access communication unit and, if the re-registration signalsare absent for a predefined period of time, issues an alarm message tothe network. The wireless access communication unit may be provided witha unique equipment identifier so that the base station can correlate thedifferent wireless links to a single wireless access communication unit.

Further embodiments, modifications, variations and enhancements of theinvention are also disclosed herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of an overall system architecture in accordance witha preferred embodiment of the present invention.

FIG. 2 is a block diagram of a basic architecture for a wireless accesscommunication unit in accordance with various aspects of the presentinvention.

FIG. 3 is a diagram of a software architecture for the wireless accesscommunication unit of FIG. 2.

FIG. 4 is a block diagram of a basic architecture for a base station.

FIG. 5 is a diagram of a software structure for the base station of FIG.4.

FIG. 6 is a block diagram illustrating addressing of multiple trunksconnected to a wireless access communication unit according to apreferred embodiment of the present invention.

FIG. 7 is a diagram illustrating an interface signaling structurebetween a base station and a base station controller.

FIG. 8 is an abstract diagram of a system protocol architecture.

FIG. 9 is a diagram illustrating a division of bearer path functionsamong a wireless access communication unit (CPRU), base station and basestation controller components of a preferred communication system.

FIG. 10 is a diagram showing interfaces between the different componentsof a preferred system.

FIG. 11 is a diagram of multiple wireless access communication units indifferent location areas connected to a single base station controller.

FIG. 12 is a call flow diagram for a network-level registrationprocedure.

FIG. 13 is a call flow diagram for a network-level de-reistrationprocedure.

FIG. 14 is a call flow diagram for a successful outgoing call setupwithout PSTN interworking.

FIG. 15 is a call flow diagram for a successful outgoing call setup withPSTN interworking.

FIG. 16 is a timing diagram of an over-the-air protocol that may be usedin the communication system shown in FIG. 1.

FIG. 17 is a timing diagram of an alternative over-the-air protocol forthe communication system shown in FIG. 1.

FIG. 18 is a diagram showing an authentication process in accordancewith a preferred embodiment of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 is a diagram showing an overall system architecture of acommunication system 101 in accordance with a preferred embodiment ofthe present invention. In the system architecture illustrated in FIG. 1,a plurality of telephone stations 102 are connected to a centraltelephone switch 105. It will be understood that telephone stations 102could comprise telephones, modems, fax machines, or other devices thatare capable of communicating over a completed call connection. Thecentral telephone switch 105 will be referred to herein as a “customerpremises equipment” or “CPE.” The CPE 105 may comprise, for example, aprivate-branch exchange (PBX) system or a key system. The design ofvarious types of PBX and key systems is well known in the art.

In the preferred embodiment depicted in FIG. 1, the CPE 105 is connectedto both a public switched telephone network (PSTN) 125 and a wirelessaccess communication unit 106 (also referred to occasionally herein, orin the drawings, as a “customer premises radio unit” or “CPRU”). Asdescribed in more detail hereinafter, in a preferred embodiment callsare selectively placed over the PSTN 125 and the wireless accesscommunication unit 106 according to the type of call. The wirelessaccess communication unit 106 communicates over a wireless trunk 108(which comprises a plurality of wireless communication links) to a basestation 109. The base station 109 is connected, along with other basestations 109 in adjacent or nearby geographical regions, to a basestation controller 112. The base station controller 112 is connected toa transcoding unit 115, which is connected to a mobile switching center(MSC) 116. Optionally, the base station controller 112 may be connecteddirectly to the mobile switching center 116, without the intermediarytranscoding unit 115. The mobile switching center 116 is connected tothe PSTN 125.

In addition to being connected to the transcoding unit 115 or,optionally, the MSC 116, the base station controller 112 is alsoconnected to an operations and maintenance center (OMC) 120, which is inturn connected to an operations support system (OSS) 122. The mobileswitching center 116 is connected to a home location register andauthentication center (HLR/AuC) 123 and to the operations support system122, as shown in FIG. 1. The base station 109 may also be connected to alocal management terminal 121.

As further described herein, the invention provides in one aspecttechniques for authentication and security in a wireless communicationsystem, such as the communication system depicted in FIG. 1. Thewireless access communication unit 106 preferably supports multipletrunks or user interface connections which are coupled to the CPE 105,and authentication is performed separately for each such trunk or userinterface connection. In one aspect, the wireless access communicationunit 106 is treated as an aggregation of individual subscribers by thenetwork. Each trunk or user interface connection supported by thewireless access communication unit 106 derives its own ciphering keybased upon an authentication parameter received from the network. Thewireless access communication unit 106 therefore provides for multipleencrypted bearer paths routed through the network, with each bearer pathhaving its own unique encryption pattern. Further details relating topreferred authentication and security techniques are described laterherein, after a description of some of the basic components of apreferred system and operation thereof.

In the preferred communication system 101 shown in FIG. 1, calls may beplaced from telephone stations 102 directly over the PSTN 125 (i.e.,over a landline connection), or over the wireless trunk 108 to the PSTN125 by utilizing the wireless access communication Unit 106. When a callis to be initiated at one of the telephone stations 102, it may berouted either directly to the PSTN 125 or to the wireless accesscommunication unit 106. The routing of the call may be either based onmanual selection, or accomplished automatically based on the numberdialed, as further described herein. In a preferred embodiment, localtelephone calls are routed directly to the PSTN 125, while long distancetelephone calls are routed through the wireless access communicationunit 106.

Operation of the system shown in FIG. 1 may depend in part on the natureof the CPE 105. As noted previously, the CPE 105 may comprise, forexample, a PBX or a key-type system. In an embodiment where the CPE 105comprises a PBX, the PBX is preferably capable of routing an outgoingcall placed from a telephone station 102 to the PSTN 125 or to thewireless access communication unit 106 based on either an access digitor the telephone number dialed by the user. The user may, for example,dial a certain first digit (e.g. an ‘8’) for access to the wirelessaccess communication unit 106, and a different first digit (e.g., a ‘9’)for direct LEC access to the PSTN 125. In this manner, the user could,for example, access the wireless access communication unit 106 to makeoutgoing long distance telephone calls, or the PSTN 125 for other typesof outgoing calls. Alternatively, some types of PBXs can be configuredto analyze the dialed number, and to route long distance and localcalls. Utilizing this ability, the PBX can be configured to route longdistance calls through the wireless access communication unit 106 andlocal or emergency calls through the PSTN 125.

In an embodiment where the CPE 105 comprises a key system, the user maymanually select a line (either for the wireless access communicationunit 106 or the PSTN 125) by depressing a key on the telephone deskset.The user could, for example, select the call processing unit 106 foroutgoing long distance calls, and the PSTN 125 for other types ofoutgoing calls. Some key systems can, like certain PBXs, be configuredto analyze the dialed number, and to route a call either to the wirelessaccess communication unit 106 or the PSTN 125 depending on the initialdigits of the call and/or the number of digits dialed. In this manner,the key system can, for example, be configured to route long distancecalls through the wireless access communication unit 106, and local oremergency calls through the PSTN 125.

In alternative embodiments, the system may be configured with lessflexibility but a potentially simpler architecture. For example, thesystem can be configured such that all incoming calls are routeddirectly from the PSTN 125 to the CPE 105, and that all outgoing localcalls (whether voice or data), all outgoing long distance data calls,and all TTY calls for persons with disabilities are also routed directlythrough the PSTN 125. In such an embodiment, the wireless accesscommunication unit 106 would generally provide outgoing long distancevoice communication capabilities.

The CPE 105 is connected to the wireless access communication unit 106across a CPE trunk interface 104. The CPE trunk interface 104 comprisesa plurality of CPE trunks, each of which may comprise, for example,loop-start trunks or ground-start trunks. The design of both loop-starttrunks and ground-start trunks is well known in the art. As is also wellknown to the practitioner in the art, both loop-start trunks andground-start trunks can be supported by the same local area switchingequipment (i.e, the same PBX or KTS).

In an embodiment in which the CPE 105 comprises a PBX, the PBXpreferably has certain operating characteristics. In addition tosupporting loop-start trunks or ground-start trunks (or both) on the CPEtrunk interface 104 between the PBX and the wireless accesscommunication unit 106, the PBX also preferably supports DTMF addresssignaling on the loop-start trunks or ground-start trunks. The PBX maybe configured to route calls through either the PSTN 125 or the wirelessaccess communication unit 106, as described previously, and thereforehas the ability to identify which trunks lead to the PSTN 125 and whichtrunks lead to the wireless access communication unit 106. The PBXpreferably has the ability to specify the order in which the trunkgroups are tried when an outgoing call is placed, and to re-routeoutgoing long-distance calls through the PSTN 125 instead of thewireless access communication unit 106 in case of access problems fromthe wireless access communication unit 106 to the wireless system.

In an embodiment where the CPE 105 comprises a key, telephone system(KTS), the KTS preferably has certain operational characteristics. Inaddition to being configured to support loop-start trunks orground-start trunks (or both) on the CPE trunk interface 104 between theKTS and the wireless access communication unit 106, the KTS alsopreferably supports DTMF address signaling on the loop-start trunks orground-start trunks, and has the ability to route calls through eitherthe PSTN 125 or the wireless access communication unit 106, as describedabove. While not essential, the KTS may also be provided withsupplementary call support features and a route selection feature (i.e.,the ability to identify trunk groups leading to the wireless accesscommunication unit 106 and the PSTN 125, and to specify on the KTS theorder in which the trunk groups should be tried). If a route selectionfeature is provided, the KTS should have the ability to re-routeoutgoing long-distance calls through the PSTN 125 instead of thewireless access communication unit 106, in case there are accessproblems from the wireless access communication unit 106 to the wirelesssystem.

The wireless access communication unit 106 acts as the gateway forwireless trunk access to the CPE 105 via the wireless system, andcorrelates the individual CPE trunks with wireless communication linkssuch that calls from the CPE 105 can be completed over a wirelessnetwork. FIG. 6 is a diagram illustrating an embodiment of a wirelessaccess communication unit 605 connected to a CPE 105 (see FIG. 1) acrossa plurality of CPE trunks 602 (in this example, four CPE trunks 602).The wireless access communication unit 605 also is connected over aplurality of wireless communication links (or ‘pipes’) 609 to a wirelessnetwork and, in particular, to a base station (not shown in FIG. 6). Thewireless access communication unit 605 establishes the wirelesscommunication links 609 and correlates therewith the CPE trunks 602, sothat communication for a particular CPE trunk 602 is carried out over anassigned wireless communication link 609. Users connected to the CPE 105can obtain access to the wireless access communication unit 605 (and,hence, to the wireless network) by being connected through the CPE 105to one of CPE trunks 602. In this manner, a potentially large number ofusers connected to the CPE 105 can have the ability to complete calls tothe wireless network, with the number of users able to make callssimultaneously equaling the number of CPE trunks 602 (and wirelesscommunication links 609) available.

Various components of the communication system shown in FIG. 1 will nowbe described in more detail. In addition, a detailed description of thepreferred system interworking, protocols and related information appearshereinafter, and also appears in copending U.S. patent application SerNos. 08/987,957, 08/988,482, 08/988,546, 08/988,262, 08/987,872, and08/987,893, each of which is filed concurrently herewith, and each ofwhich is hereby incorporated by reference as if set forth fully herein.

The wireless access communication unit 106, as noted, acts as thegateway for the CPE 105 to the wireless network, and preferably performsa variety of functions. In a preferred embodiment, the wireless accesscommunication unit 106 performs off-hook-detection for outgoing callsand supports provision of a dial tone to the CPE 105 (and thereby to thetelephone station 102 initiating the call). The wireless accesscommunication unit 106 also initiates acquisition of a wirelesscommunication channel (such as an over-the-air time slot, for example,if the wireless network is a TDMA and/or TDD system), and initiates callcontrol procedures. During call establishment, the wireless accesscommunication unit 106 detects dialed address digits (i.e., DTMF tones)and passes the received digits via call control signaling to thenetwork. The wireless access communication unit 106 decides whether tolaunch a normal or emergency call depending upon an end-of-dialingindication received from the base station 109 indicating the type ofcall (based on digit analysis performed at the base station 109). Inaddition, the wireless access communication unit 106 detects off-hooktransitions from the CPE 105, and initiates call release procedurestowards the network in response to an off-hook transition. When a callis completed, the wireless access communication unit 106 provideslandline-transparent control of disconnect procedures for clearinginitiated by the CPE 105. As part of this function, the wireless accesscommunication unit 106 implements the release guard times supported byconventional wireline systems.

In addition to the above functions, the wireless access communicationunit 106 also supports the signaling of DTMF digits during an activecall. As part of this function, the wireless access communication unit106 detects DTMF tones from the CPE 105 during an active call and relaysthe digits to the network via DTAP signaling. Also during a call, thewireless access communication unit 106 may pass call progress tonesreceived from the network transparently over the bearer path to the CPE105. Whenever call progress DTAP signaling is received from the network,the wireless access communication unit 106 converts the call progressDTAP signals into call progress tones towards the CPE 105. The wirelessaccess communication unit 106 may generate reorder tones to the CPE 105when needed, so as to indicate congestion of the wireless network orpermanent signal timer expiry conditions to the CPE 105.

Additionally the wireless access communication unit 106 also preferablyperforms a number of functions related to bearer processing. Forexample, in a preferred embodiment the wireless access communicationunit 106 performs vocoding for voice communication. In this regardvocoding includes encoding/compression of speech towards the network anddecoding/de-compression of speech in the reverse direction (i.e.,towards the CPE 105). The wireless access communication unit 106 alsopreferably performs forward error correction (FEC), encryption anddecryption for the bearer voice (with the wireless access communicationunit 106 and transcoding unit 115 being peer-to-peer endpoints forciphering) and echo cancellation functions. For encryption anddecryption, the wireless access communication unit 106 encrypts thebearer data prior to transmission over the air (i.e. over the wirelesstrunk 108), and decrypts bearer data received from the network. Echocancellation functions are supported by the wireless accesscommunication unit 106 so as to suppress the echo potentially generatedtowards the wireless network if, for example, a 2-4 wire hybridstructure is present at the interface with the CPE 105.

In a preferred embodiment, the wireless access communication unit 106 inconjunction with the wireless system supports management and securityfeatures such as call registration. de-registration, userauthentication, ciphering of bearer information, and network managementfunctions. In addition to providing a means for outgoing voice calls,the wireless access communication unit 106 may also support outgoingemergency (i.e., “911”) calls and end-to-end DTMF signaling duringactive calls.

Details of a preferred wireless access communication unit 201 aredepicted in FIG. 2, and of a preferred software structure for thewireless access communication unit 201 in FIG. 3. As shown in FIG. 2,the wireless access communication unit 201 comprises a plurality ofsubscriber ports 203, which are provided for connecting the CPE 105 (seeFIG. 1) to the wireless access communication unit 201 across a trunkinterface (e.g., trunk interface 104 shown in FIG. 1). Each subscriberport 203 can support one call connection over the wireless accesscommunication unit 201, and may comprise, for example, an RJ-11interface. While four subscriber ports 203 are shown in FIG. 2, it willbe understood that the number of subscriber ports 203 may vary dependingupon the particular application or environment in which the wirelessaccess communication unit 201 is deployed. For example, the wirelessaccess communication unit 201 may be configured with only a singlesubscriber port 203, or may have any number of subscriber ports 203limited only by practical considerations such as the number of wirelesscommunication channels generally accessible and available to thewireless communication unit 201. Also, the subscriber ports 203 maycomprise any suitable interface, with an RJ-11 interface being but oneexample of such an interface.

Each subscriber port 203 is connected to an individual line interfaceunit or line card section 205. Thus, the wireless access communicationunit 201 comprises four line card sections 205, one for each subscriberport 203. The line card section 205 provides a physical subscriber lineinterface from the CPE 105 to the wireless access communication unit201, and in addition provides digitizing and data compression functions.

Details of one of the multiple line card sections 205 are shown in FIG.2, with the other line card sections 205 being configured in a similarfashion. The line card section 205 comprises a subscriber interface 207which is connected to one of the subscriber ports 203. The subscriberinterface 207 comprises a subscriber line interface circuit (SLIC) 217,which provides conventional loop interface functions including batteryfeed, overload protection, supervision, and 2-4 wire hybrid. Bothloop-start and ground-start signaling are preferably supported by theline card section 205. The selection between loop-start and ground-startsignaling may be made, for example, by use of a manual toggle switch ordip switch (not shown) located on the wireless access communication unit201, each line card section 205 may be individually configured tointerface with a loop-start or ground-start trunk. The subscriberinterface 207 further comprises a standard CODEC or, alternatively, asubscriber line audio processing circuit (SLAC) 215 which carries outanalog-to-digital and digital-to-analog conversion between the line cardsection 205 and the user station (e.g., telephone station 102 shown inFIG. 1) connected to the subscriber port 203. The CODEC or SLAC 215provides a standard μ-law pulse code modulation (PCM) interface. Thesubscriber interface 207 also comprises a ring generator 216 forgenerating a ringback tone.

A digitized data stream is output from the CODEC or SLAC 215 andprovided across signal line(s) 214 to a vocoder 206, which compressesthe digitized data stream into a compressed data signal. The vocoder 206comprises a relatively high-speed digital signal processor 211(operating at, e.g., a rate of twenty million instructions per second orother suitable rate), along with support modules such as a high-speedstatic random-access memory (SRAM) 212 and an EPROM 213. The vocoder 206preferably provides, as part of its decoding function, an interpolationcapability for deriving predicted speech patterns, so as to handlesituations where, for example, the wireless access communication unit201 detects data frames that contain errors, or else the data framescontain errors that cannot be corrected by forward error correction(FEC). The decoding function of the vocoder 206 also preferably providesa mute capability for silencing the output to the CPE 105 whenbeneficial to do so. such as during control traffic exchanges. Thevocoder 206 outputs a compressed data signal at a rate of, e.g., 8 Kbps,which is sent to a control line card assembly (LCA) 226 located in acontrol section 220. Control section 220 thereby receives fourcompressed data signals, one from each of the line card sections 205.

Each line card section 205 also hosts a subscriber interface module(SIM) 208. The general functions of the SIM 208 are to provide systemsecurity and store subscriber-specific information, including suchthings as subscriber authentication information and subscriber-specificdata. In a preferred embodiment, the SIM function is duplicated for eachCPE trunk supported by the wireless access communication unit 201, aseach CPE trunk may be viewed as a different subscriber by the network.This duplication may be explained with reference to FIG. 6. In FIG. 6, aplurality of CPE trunks 602 are shown connected to the wireless accesscommunication unit 605 (each CPE trunk 602 being connected to asubscriber port 203 shown in the more detailed diagram of FIG. 2). Aseparate SIM 606 is associated with each of the CPE trunks 602. Thus,for four CPE trunks 602, the wireless access communication unit 605comprises four SIMs 606. The wireless access communication unit 605further comprises a plurality of radio interface units 607, one for eachof CPE trunk 602, for the purpose of passing data and other informationto the wireless transceiver (not shown) which handles the physicalwireless communication links 609.

Generally, each subscriber within the communication system requiresunique identification and possibly different system parameters. To theextent that the multiple CPE trunks (corresponding to the multiplesubscriber ports 203 shown in FIG. 2) are viewed by the system asindividual and unique subscribers each CPE trunk is associated with aunique identifier and, preferably, unique authentication and othersystem parameters, which are implemented at least in part with theseparate SIM 208 used in each line card 205. Thus, for four CPE trunks(corresponding to the four subscriber ports 203 shown in FIG. 2), fourcopies of the SIM 208 are used in the wireless access communication unit201.

The functionality of the SIM 208 may be implemented as one or morenon-removable SIM chips within the wireless access communication unithardware architecture. The SIM 208 stores within a non-volatile memory(such as a ROM, or non-volatile RAM) subscriber information such as asubscriber identifier. In a preferred embodiment, the subscriberidentifier comprises an international mobile subscriber identity (IMSI)number. In addition to storing the subscriber identifier, the SIM 208also runs an authentication procedure such as. for example, an “A3”and/or “A8” authentication procedure conventionally used in certain GSMapplications. The details of preferred authentication procedures aredescribed later herein.

The control section 220 of the wireless access communication unit 201provides timing and control for virtually all aspects of the wirelessaccess communication unit 201. The control section 220 comprises aprocessor 225 which may comprise, for example, a 16-bit RISC processor(such as a C165 or C163 processor manufactured by Siemens Corp.) andassociated support modules (i.e., SRAM, flash memory, etc.). Access tothe SIM 208 is initiated by the host processor 225 and controlled andformatted by the control line card assembly (LCA) in the control section220. The processor 225 also coordinates most system activities and movesdata between the various modules.

The processor 225 is connected to the control LCA 226 which, as notedabove, is connected to the vocoder 206 from each of the line cardsections 205. The control LCA 226 is also connected to a radio interfaceline card assembly (RIF LCA) 227. The control LCA 226 provides theinterface between the radio section and the line card section of thewireless access communication unit 201. The control LCA 226 packages andformats data, and coordinates and controls the over-the-air (OTA)protocol. It thereby maintains coordination between up to fourcompressed serial data streams (one from each of the line card sections205) and their respective over-the-air communication channels.

The radio interface LCA 227 is connected to a baseband processor 228,which may include a digital radio ASIC (DRA) 229. The baseband processor228 is connected to a radio section 240. The radio section 240preferably comprises a plurality of antennas 243 which are selectable bya selector 242 which is connected to the control LCA 226. Signals fromone or more antennas 243 are thereby provided to a radio transceiver 241(possibly including multiple radio receivers, one for each antenna 243).In a preferred embodiment, antenna diversity techniques are utilizedsuch that the wireless access communication unit 201 selects the bestantenna (and/or radio receiver) for each frame of time in which itcommunicates. Various antenna selection techniques are known in the art,or are described in, for example. U.S. patent application Ser. No.08/826,773 filed Apr. 7, 1997, hereby incorporated by reference as ifset forth fully herein.

The wireless access communication unit 201 may be powered either throughan external DC power supply 250 or an on-board battery 251. The battery251 may be used as a reserve power supply, being brought into serviceautomatically if the external DC supply 250 is cutoff or otherwiseunavailable. A power section 221 for the wireless access communicationunit 201 may comprise local voltage regulators to supply required powerto the logic and radio sections, and a switching regulator to supply anyrequisite loop battery voltage.

The wireless access communication unit 201 may be provided with an LED231 or other visual display mechanism(s) to indicate the status of thedevice to an observer. The types of status conditions to be displayedmay include, for example, whether the power is on, whether the device isfunctional (i.e., all self tests have been passed), or whether thedevice is in service (i.e., is currently registered with a basestation).

In operation, compressed serial data is transferred to and from themultiple line cards 205 under the direction of the control LCA 226. Thecontrol LCA 226 places the compressed serial data in a format suitablefor the radio interface LCA 227. It also performs any desired encryptionor adds forward error correction information. The control LCA 226transfers the data to the radio interface LCA 227 which passes the datato the baseband processor 228. The radio interface LCA 227 keeps trackof channel and timing information, and instructs the baseband processor228 to process the data according to the channel and timing parameters.In a preferred embodiment, the baseband processor 228 comprises atransmitter for formulating continuous phase modulated spread-spectrumsignals, or other types of quadrature or related signals, as described,for example, with respect to transmitters shown in U.S. Pat. Nos.5,629,956, 5,610,940 or 5,548,253, all of which are hereby incorporatedherein by reference as if set forth fully herein. At the appropriatetime intervals, as determined by the radio interface LCA 227, thebaseband processor 228 sends the data to the radio section 240 whichconverts the signal to the appropriate transmission frequency andperforms any necessary filtering for transmission over the air. Thefrequency band utilized by the wireless access communication unit 106 isgenerally dictated by the overall communication system within which theunit is deployed. For example, the frequency band may be within the PCSfrequency band of 1930 MHz to 1990 MHz, or may be any other suitablefrequency band or bands.

Incoming message signals are received by one or more of antennas 243 andsent to the radio transceiver 241 for downconversion and/or filtering asneeded. The downconverted and/or filtered data is then sent to thebaseband processor 228 which demodulates the received signal. In apreferred embodiment, the wireless access communication unit 201transmits and receives messages using a spread spectrum format. In suchan embodiment, the baseband processor 228 preferably comprises a spreadspectrum correlator. A wide variety of spread spectrum correlators areknown in the art, examples of which include embodiments illustrated ordescribed in U.S. Pat. Nos. 5,629,956, 5,610,940, 5,396,515 or5,499,265, each of which is hereby incorporated by reference as if setforth fully herein.

The baseband processor 228 outputs, among other things, a receivedsignal strength indicator (RSSI), which is used by the control LCA 226in selecting the best antenna 243 (and/or radio receiver) for receptionof the incoming signal. After spread spectrum correlation, the basebandprocessor 228 provides a stream of data bits to the radio interface LCA227, which transfers the data to the appropriate line card 205 basedupon the over-the-air communication channel over which the data wasreceived. The data is then processed by the line card 205 and sent tothe CPE 105 via the particular subscriber port 203 connected to the linecard 205.

A diagram of a preferred software structure for the wireless accesscommunication unit 201 is shown in FIG. 3. As shown in FIG. 3, thesoftware of the wireless access communication unit 201 is functionallydivided into two main components, based on the physical interfacessupported by the wireless access communication unit 201. These two maincomponents are referred to in FIG. 3 as the line manager 350 and theover-the-air manager 351.

The line manager 350 generally handles the CPE trunk management andcommunication between the wireless access communication unit 201 and theCPE 105. In addition to CPE trunk management and communication interfacefunctions, the line manager 350 is also responsible for call signaling,DTMF recognition, and transfer of collected DTMF digits to theover-the-air manager 351. The line manager 350 comprises a plurality ofline drivers 303 and a plurality of SIM drivers 304, one line driver 303and one SIM driver 304 for each CPE trunk supported by the wirelessaccess communication unit 201. A single line driver 303 and SIM driver304 collectively comprise a CPE line software component 302.

The over-the-air manager 351 handles the communication interface andlink management to the base station 109 (see FIG. 1). The over-the-airline manager 351 is also responsible for receiving DTMF digits from theCPE 105 (via the line manager 350) and relaying the DTMF digits to thebase station 109 (which ultimately conveys them to the PSTN 125), as setforth in more detail copending U.S. patent application Ser. No.08/987,893, previously incorporated herein by reference. Theover-the-air line manager 351 also implements the over-the-aircommunication protocol, including end-to-end communication with variousnetwork entities such as the base station controller 112 and mobileswitching center 116 (shown in FIG. 1). Exemplary over-the-aircommunication protocols that may be implemented by the over-the-airmanager 351 include, for example, the GSM direct application transferpart (DTAP) protocol, or the IS-661 over-the-air (“O-Notes”) protocol asdescribed in the OMNI_Notes_RMT Protocols Rev. 02.03D (release date Jun.30, 1997), appearing as a Technical Appendix A filed herewith, andhereby incorporated by reference as if set forth fully herein. At thephysical radio level, the over-the-air manager 351 of the wirelessaccess communication unit 201 preferably implements the IS-661 protocolas set forth in the above-referenced OMNI_Notes_RMT Protocolspublication, or a variation thereof.

As further illustrated in FIG. 3, the over-the-air manager 351 comprisesa plurality of CPE line link objects 310, one for each CPE trunk (i.e.,subscriber port 203) supported by the wireless access communication unit201. Each CPE line link object 310 provides the signaling resource for asingle CPE line or trunk, and comprises several components whichtogether form a signaling protocol stack. The components of thesignaling protocol stack work together to interface with a CPE line toprovide call management, mobility management and radio resourcefunctionality required to complete a voice call, and the registrationfunctionality required to utilize network resources.

Each CPE line link object 310 comprises a CPE line manager 311, thepurpose of which is to interface with the CPE line software component302 for the appropriate CPE line or trunk. In a preferred embodiment,the CPE line manager interfaces with a GSM call management component 312and a GSM call registration component 313, both of which interface witha GSM mobility management component 314. The GSM mobility managementcomponent 314 interfaces with a protocol adaption (PAL) component 315,which interfaces with an over-the-air state (OTA) machine 316. The OTAstate machine 316 is generally responsible for managing the physicalradio interface, and communicates with the radio transmit/receiverinterface and slot management (RTRX) component 321.

In operation, the CPE line manager 311 signals the GSM mobilitymanagement component 314 to initiate connection establishmentprocedures, as described in more detail hereinafter with respect to thecall flow diagrams appearing in FIGS. 13 through 22. The CPE linemanager 311 also controls transmission of DTMF digits to the network,the enabling of the speech path, generation of ringback tones,generation of a busy tone (in non-PSTN interworking situations), andpassing of on-hook indication to the CPE 105. In addition, the CPE linemanager 311 manages CPE-initiated call clearing as well as normal andemergency call procedures.

The GSM call management component 312, GSM registration component 313,and GSM mobility management component 314 provide a degree of GSMfunctionality relating to call management, registration, and mobilitymanagement, respectively. The protocol adaption component 315 adapts, ifnecessary, the GSM signaling protocol to the over-the-air protocol (suchas, for example, to the IS-661 over-the-air protocol). The OTA statemachine 316 implements the over-the-air protocol and, as noted, managesthe physical radio interface.

In addition to the multiple CPE line link objects 310, the OTA manager351 further comprises a hardware services component 320 which provides aprogramming interface to the hardware (including hardware controlled bythe line drivers 303 and SIM drivers 304) of the wireless accesscommunication unit 201. The OTA manager 351 may comprise a real-timeoperating system (RTOS) 330, which may be a multi-tasking operatingsystem, as well as a power-on/reset initialization (POST) component 323and a debug port manager 322. The debug port manager 322, if provided,allows access externally to the internal status of the software, andalso permits software downloads.

In addition to the above-described components, the OTA manager 351 alsocomprises an operations, administration and management (OAM) component324. The OAM component runs at the application level, and performs suchfunctions as recognition of faults, creating and sending alarms, andcommunicating with the line manager 350 for call processing data neededin fault detection and alarms. The types of faults or failures monitoredmay include, for example, hardware failures (such as power supplyfailures, radio unit failures, line card failures, and so on), softwarefailures, communication failures, and quality of service failures (e.g.,unsuccessful call attempts per time period, time slot interchangerequests per time period, unsuccessful time slot interchanges per timeperiod, number of dropped calls per time period, channel quality asindicated by bit error rate, and so on), among others. Fault reportingmay be coordinated such that a single fault that causes multiplefailures due to the dependency of the software, hardware and telecomfunctions will result in a single fault being reported.

In one aspect, the functionality of the over-the-air manager 351 used tosupport the wireless access communication unit 201 may be viewed as asubset or modification of the functionality that would be used tosupport a mobile user application. For example, the mobility managementinterface (MMI) software component used in a conventional GSM system tosupport a mobile user is, in the software architecture shown in FIG. 3,replaced with a CPE line manager 311. Another difference over a mobileuser application is that a logical instance of the signaling protocolstack is provided for each CPE line connected to the wireless accesscommunication unit 201 (as opposed to having a single logical instanceof the signaling protocol stack for a mobile user application), and theSIM driver is modified offer a mobile user application to accommodatemultiple SIMs (or their logical equivalents) by, for example, theprovision of multiple independent SIM drivers 304. Further, an abilityis added to associate a hardware voice path from the CPE 105 with a basestation communication link. The signaling protocol may also be modified,as further described herein, to support digit analysis by the basestation 109 (see FIG. 1). DSAT and DTA adaptor software componentsconventionally used in certain mobile user applications are not neededby the wireless access communication unit 201, and are therefore notimplemented.

Referring back to FIG. 1, the wireless access communication unit 106interfaces with a base station 109 of the wireless system to achieveaccess to the PSTN 125. A block diagram of a preferred base station 401is shown in FIG. 4. The base station 401 comprises a number of separatecomponents connected together by a common global bus backplane, asillustrated in FIG. 4. These components include a digital line card 404,an over-the-air (OTA) processor card 405, a power supply module 407, anda plurality of radio cards 406, all of which reside on an electronicsmodule 420. The electronics module 420 is connected to an I/O module421, which comprises protection circuitry 403 to prevent such things asdamage from short circuits. Each radio card 406 is connected, via theprotection circuitry 403, to one of a plurality of antennas 403. Thedigital line card 404 is connected, via protection circuitry 403, to thePSTN 125 (through base station controller 112 and MSC 116, as shown inFIG. 1) over a backhaul line 430, and possibly to other base stations109 as well over other physical connections. The base station 401 may beconnected to a local AC power supply line 425, if available.

In operation the wireless access communication unit (identified byreference numeral 412 in FIG. 4) transmits over-the-air messages to andreceives over-the-air messages from the base station 401. The multipleantennas 411 and radio cards 406 are used at the base station 401 forachieving antenna diversity. Typically one antenna 411 is selected at agiven time for transmitting or receiving over-the-air signals. If spreadspectrum communication is being used, then the OTA processor card 405may comprise a spread spectrum correlator and other baseband processingcircuitry for correlating a spread spectrum signal received from thewireless access communication unit 412 and converting it to data bits.The OTA processor card 405 transfers data to the digital line card 404,which formats the data and sends it over a backhaul to the PSTN 125 viathe other intervening system components (such as the base stationcontroller 112 and MSC 116). Similarly, the digital line card 404receives data from the PSTN 125, and transfers the data to the OTAprocessor card 405 which formats the data for the over-the-air protocoland transmits the formatted data using a selected radio card 406 andantenna 411.

The primary functions of the radio cards 406 are to transmit and receiveRF data packs, to perform packet data integrity services (e.g., cyclicredundancy checks), and to support antenna diversity algorithms. Theprimary function of the OTS processor card 405 is to move bearer databetween the radio cards 406 and the digital line card 404. The OTAprocessor card 405 also executes operations, administration, managementand provisioning (OAM&P) requests from the digital line card 404,communicates signaling information (using internal base station messagesor “I-Notes”) with the digital line card 404, and communicates signalinginformation (using over-the-air signaling messages or “O-Notes”) withthe wireless access communication unit 412. Various types of signalinginformation and formats therefor (including I-Notes and O-Notes) thatmay be transmitted across or within the base station 401 or other systemcomponents are described in, for example, copending U.S. patentapplication Ser. No. 08/532,466 filed Sep. 22, 1995, hereby incorporatedby reference as if set forth fully herein.

The primary functions of the digital line card 404 are to handle linkaccess procedures for the “D-channel” (LAPD) transport on the backhaulline 430, to exchange bearer data between the OTA processor card 405 andthe network-side backhaul components (such as the base stationcontroller 112), and to multiplex and demultiplex bearer data on thebackhaul line 430. Other primary functions of the digital line card 404include synchronizing the over-the-air bearer frame timing with thetiming on the backhaul line 430 (such as a T1 line), to providetranslation between the OAM&P procedures supported on the network andradio interfaces, to map internal base station messages (e.g., I-Notes)to/from the LAPD transport on the backhaul, and to communicate signalinginformation (using, e.g., signaling I-Notes) with the OTA processor card405.

A preferred high level software architecture for the base station 401 isdepicted in FIG. 5. According to the software architecture shown in FIG.5, the software of the base station 401 is split into two functionalgroups, one functional group relating to the over-the-air functions andthe other functional group relating to the line card functions. Thesetwo main functional groups are shown in FIG. 5 as the OTA manager 502and the line card manager 503, each of which preferably runs on its ownprocessor board. Further information regarding the software architecturefor the base station 401 may be found in the copending patentapplications previously incorporated herein by reference.

Various interfaces associated with the base station 401 are showndiagrammatically in FIG. 5 as dotted lines, and include an over-the-airinterface or “O-interface” 560 between the wireless access communicationuntil 412 and the base station 401, an internal interface or“I-interface” or “N-interface” 562 between the base station 401 and thenetwork-side backhaul components (such as the base station controller112, MSC 116, and PSTN 125 shown in FIG. 1). Further informationregarding these interfaces may be found in copending U.S. patentapplication Ser. Nos. 08/988,482 and 08/988,546, previously incorporatedherein by reference. These interfaces are also shown at an abstractlevel in FIG. 10, described later herein.

In operation, the base station 401 manages the radio resources for thewireless access communication unit 412, and thereby provides support forthe network side of the wireless trunk 108 (see FIG. 1). A wide varietyof different communication schemes and radio resource protocols may beused. If, for example, the base station 401 implements an IS-661protocol for over-the-air communication, then the base station 401manages the resources necessary to support the wireless communicationchannels between the wireless access communication unit 412 and the basestation 401, including time slots and spread spectrum codes. The basestation 401 also provides multiplexing functions for the transfer ofdata to and from the backhaul line 430 providing the connection to thePSTN 125. The base station 401 may, for example, multiplex data over aT1 (or fractional T1) backhaul line 430 to the base station controller112, which, as noted, pipes the data to and from the PSTN 125 via theMSC 116.

Protocol signaling over the N-Interface 562, which connects the basestation 401 (or 109 in FIG. 1) to the base station controller 112 (seeFIG. 1), may be transported using the Q.921 LAPD protocol. Protocolsignaling over the O-Interface 560, which connects the base station 401to the wireless access communication unit 412, may be accomplished usingover-the-air signaling messages (“O-Notes”) according to the IS-661protocol. The O-Notes may be transmitted along with bearer data inIS-661 RF packets.

The base station 401 connects and manages radio and terrestrial bearerchannels for call-related features, and supports system administrationvia OAM&P controlled by the system operator through the operationsmanagement center 120 (see FIG. 1). As part of its radio resourcemanagement functionality, the base station 401 supports outgoing voicecalls (normal and emergency) from the wireless access communication unit412. Incoming pages to the wireless access communication unit 412 mayoptionally be supported by the base station 401.

Among its other radio resource management functions, the base station401 manages mapping of the radio channels (including the wirelesscommunication channels of the wireless trunk 108) to the terrestrial(i.e., backhaul) channels. The base station 401 also provides. throughits OAM&P functionality, support for administrative state changes,configuration, and provisioning of the radio resources. The base station401 also provides fault management and alarm management for the radioresources, and sends fault or alarm signals to the base stationcontroller 112. In addition, the base station 401 provides signalingflow control across the over-the-air interface, power control managementfor each radio channel radio link recovery upon radio link interruption,and debug information logs to the base station controller 112 As part ofits power control management for the various radio channels, the basestation 401 may send performance metrics relating to the radio resourcesto the base station controller 112 for analysis.

In terms of call control support, the base station 401 is involved inestablishing, maintaining and tearing down outgoing voice calls receivedfrom the wireless access communication unit 412. The base station 401provides digit analysis for outgoing telephone calls, and relays DTMFsignaling from the end user to the PSTN 125, if necessary, during anactive telephone call. This signaling is relayed transparently throughthe base station 401, and is supported by the I-interface andN-interface transport procedures.

The base station 401 also preferably provides security support invarious manners. The base station 401 may, for example, provide supportfor bearer ciphering that occurs at the transcoding unit 115 and thewireless access communication unit 106. The base station 401 may alsosupport the GSM temporary mobile subscriber identity (TMSI) forprotection of the user identity.

Referring again to FIG. 1, aspects of the base station controller 112will now be described. As shown in FIG. 1, the base station 109 isconnected to the base station controller 112 over an interface such asan N-interface (such as the N-interface 562 described previously withrespect to FIG. 5). Data (including signaling messages and bearertraffic) are passed between the base station 109 and the base stationcontroller 112 across the N-interface.

A preferred base station controller 112 may be viewed in one aspect as abase station subsystem controller that is used for managing one or morebase stations 109. A primary responsibility of the base stationcontroller 112 is to provide an interface between the MSC 116 and theradio access subsystem (i.e., the system components responsible forestablishing and maintaining the physical radio channels). In apreferred embodiment, the base station controller 112 incorporatesaspects of the IS-661 communication protocol and the GSM communicationprotocol, thereby using what may be referred to as a “hybrid” protocol.Details of a preferred communication protocol may be found in, forexample, copending U.S. patent application Ser. Nos. 08/988,482 and08/988,546, previously incorporated herein by reference. In analternative embodiments, the base station controller 112 may beimplemented using the IS-661 protocol in its entirety, or the GSMcommunication protocol in its entirety.

In a communication system using a “hybrid” protocol having aspects ofboth IS-661 and GSM protocols, the base station controller 112preferably performs a variety of resource management functions. As partof these functions, the base station controller 112 switches bearercircuits and provision of bearer connectivity to form a path from thebase stations 109 to the MSC 116 for outgoing voice calls from thewireless access communication unit 106. IN addition to switching bearercircuits, the base station controller 112 provides signaling paths fromthe wireless access communication unit 106 to the MSC 116 and othernetwork elements. If required, the base station controller 112 carriesout the interworking between the BSSMAP radio resource managementprocedures on the GSM A-interface 571 and the “N-Notes” radio resourcemanagement procedures on the N-interface 562.

The base station controller 112 is involved in the allocation andrelease of radio channels. If the IS-661 protocol is used, then the basestation 109 is the entity that actually assigns and releasesover-the-air resources. As part of call setup, however, the base stationcontroller 112 is the entity that coordinates this process. The basestation controller 112 also controls the allocation and release ofbackhaul channels. If the IS-661 protocol is used, then the base station109 is the entity that actually assigns the bearer resources over thebackhaul channels. However, as part of call setup, the base stationcontroller 112 coordinates this process as well.

The base station controller 112 is also involved in ciphering oftransmitted data. While the Transcoding unit 115 (see FIG. 1) ispreferably the network end-point for bearer ciphering, the base stationcontroller 112 sets up and coordinates ciphering of bearer messages.

Certain mobility management procedures, such as authentication andidentification, run end-to-end between the wireless access communicationunit 106 and the MSC 116, and are relayed through the base stationcontroller 112 with essentially no interworking requirements. For othermobility management functions, the base station controller 112 performsinterworking between the N-interface and A-interface procedures. Forexample, the base station controller 112 may perform interworkingbetween the N-interface and A-interface procedures for location updatingor network-level registration (both normal and periodic, as furtherdescribed herein), de-registration or IMSI detach, time slot interchangereallocation, and mobility management connection establishment.

Call control messages and procedures run end-to-end between the wirelessaccess communication unit 106 and the MSC 116, and are relayedtransparently through the base station controller 112. In one aspect,the base station controller 112 provides a signaling path between thewireless access communication unit 106 and the MSC 116 to carry out callcontrol signaling.

The base station controller 112 may support a variety of interfaces. Thebase station controller 112 preferably supports the T-interface to thetranscoding unit 115 or, if the transcoding unit functionality isconsolidated with the base station controller 112, a GSM A-interfacebetween the consolidated base station controller/transcoding unit andthe MSC 116. In the other direction, the base station controller 112also preferably supports the N-interface to the various base stations109 to which it is connected.

In a preferred embodiment, the base station controller 112 transmits andreceives information to the transcoding unit 115, shown in FIG. 1. Thetranscoding unit 115 in one aspect comprises a base station subsystem(BSS) entity located, in one embodiment, between the base stationcontroller 112 and the MSC 116. Preferably, the transcoding unit 115 isunder management control of the base station controller 112, but isphysically located on the premises of the MSC 116, thereby allowing thebase station controller 112 to be remotely located from the site of theMSC 116. The transcoding unit 115 comprises a number of transcoding unitshelves, operating independently of one another but under the control ofthe base station controller 112. In a preferred embodiment, eachtranscoding unit shelf supports up to 92 bearer channels.

The transcoding unit 115 generally provides the network side processingof key functions on the bearer path. This processing may include, forexample, speech transcoding, network-side forward error correction(FEC), and network-side enciphering and deciphering of bearer voice.

With respect to the speech transcoding function, the transcoding unit115 preferably provides bidirectional conversion between encoded voicedata received from the user side, and “mu-law” coded pulse-codemodulated (PCM) data received from the network side at 64 kilobits persecond. The vocoder 206 in the wireless access communication unit 106(see FIG. 2) compresses speech received from the CPE 100 forover-the-air transmission towards the network. In the reverse direction,the vocoder 206 in the wireless access communication unit 106de-compresses over-the-air speech prior to transmission to the CPE 105.

The transcoding unit 115 preferably comprises, among other things, aspeech encoder and speech decoder. The speech encoder in the transcodingunit 115 receives PCM speech data from the network delivered at 64kilobits per second, and compresses this data into a sub-rateover-the-air channel for transmission towards the wireless accesscommunication unit 106. Forward error correction (FEC) information isadded separately at the transcoding unit 115 by the FEC function. Thespeech decoder in the transcoding unit 115 processes compressed speechdata from the wireless access communication unit 106, and transcodesthis data to produce 64 kbit/s PCM speech data for transmission towardsthe MSC 116. The speech decoder in the transcoding unit 115 additionallyprovides an interpolate function to output predicted speech patterns, inthe event that the base station 109 detects frames that contain errorsthat are not correctable by the forward error correction function. Thespeech decoder in the transcoding unit 115 also provides a mutecapability for silencing the output to the A-interface when necessary,such as during control traffic transmissions.

With regard to forward error correction (FEC), in the user-to-networkdirection the FEC information is added on to messages by the wirelessaccess communication unit 106. The channel decoding function in the basestation controller 112 and/or transcoding unit 115 uses the FECinformation to detect the presence of errors, and to estimate the mostprobable emitted bits given the received ones. In the network-to-userdirection, the base station controller 112 and/or transcoding unit 115applies forward error correction on the frames received from thevocoding function, before the frames are sent across the N-interface.The FEC decoding in the network-to-user direction is performed by thewireless access communication unit 106.

With regard to encryption and decryption functions, a bearer encryption(or ciphering) mechanism utilized in the system is preferably based onthe GSM A5/1 algorithm, which is an algorithm well known in the art. Forbearer speech, the two endpoints in the system for encryption anddecryption are the wireless access communication unit 106 and thetranscoding unit 115. Where communication is divided into time framesand time slots (such as in certain types of time division multipleaccess or TDMA systems), encryption and decryption may be performed on aper-frame basis.

The wireless access communication unit 106 and the transcoding unit 115preferably are “encryption synchronized” in the sense that the framenumber used by the wireless access communication unit 106 to encrypt aframe is the same as the frame number used by the transcoding unit 115to decrypt, and vice versa. The GSM A5/1 algorithm involves thegeneration of encryption/decryption masks on a per-frame basis, based onthe frame number. Typically, establishment or re-establishment ofencryption synchronization occurs at call setup and when recovering fromloss of encryption synchronization due to error conditions (whetherexperienced in the over-the-air link or the backhaul link). Once theencryption synchronization is established (or re-established, as thecase may be), the wireless access communication unit 106 and thetranscoding unit 115 increment the frame number for each frame cycle onthe over-the-air and backhaul interfaces. Preferably, the same framelength (e.g., 20 milliseconds) is used for both the over-the-air and thebackhaul time frames, so incrementing the frame number each frame cyclenormally maintains frame number synchronization between the twoendpoints of the encryption/decryption function.

The transcoding unit 115 may support a variety of interfaces. Thetranscoding Unit 115 may support the A-interface linking the transcodingunit 115 at the MSC 116 and the T-interface linking the transcoding unit115 to the base station controller 112. The T-interface carries bearervoice data that is processed by the transcoding unlit bearer functionsand relayed on the A-interface to the MSC 116, as well as A-interfacesignaling over SS7 links. Preferably, the transcoding unit 115 providestransparent pass-through of signaling between the base stationcontroller 112 and MSC 116 over SS7 links and, optionally, X.25 orsimilar type links. The T-interface also carries signaling for OAM&Pcontrol of the transcoding unit 115, and inband signaling between thetranscoding unit 115 and the base station controller 112 for dynamicper-call control of the transcoding unit functions. Signaling exchangedbetween the transcoding unit 115 and the base station controller 112 isconcentrated in a specific time slot (e.g., the first time slot of atime frame), and controlled through the level-2 link-access proceduresfor the D-channel (LAPD) protocol.

FIG. 9 is a high level diagram illustrating a preferred breakdown ofbearer path functions performed at the wireless access communicationuntil 106, the base station 109, and the base station controller 112and/or transcoding unit 115. As shown in FIG. 9, the wireless accesscommunication unit bearer path functions 901 include voice encoding anddecoding 911, forward error correction (FEC) 912, encryption anddecryption 913, and tone generation 914. The base station bearer pathfunctions 902 include backhaul framing 921 and channel multiplexing anddemultiplexing 922. The base station controller and transcoding unitbearer path functions 903 comprise voice encoding and decoding 931,forward error correction (FEC) 932, encryption and decryption 933,backhaul framing 934, and channel multiplexing and demultiplexing 935.These functions have been mentioned previously in relation to thevarious components of the system, and are further described in variouslevels of detail elsewhere herein or in materials incorporated byreference herein.

As shown in FIG. 9, the speech encoding/decoding, encryption/decryptionand FEC functions performed in the wireless access communication unit106 are mirrored in the based station controller 112 and/or transcodingunit 115. The channel multiplexing/de-multiplexing and backhaul framingfunctions performed in the base station 109 are also mirrored by thebase station controller 112 and/or transcoding unit 115.

Referring again to FIG. 1, the transcoding unit 115 is connected to themobile switching center (MSC) 116, which is connected to the PSTN 125.The MSC 116 is a cellular switch that acts as an interface between thebase station subsystem (BSS) and the PSTN 125, and acts as the gatewayto the long-distance network. The MSC 116 has telephone exchangecapabilities including call setup, routing selection, switching betweenincoming and outgoing channels, control of communications, and releaseof connections. In addition, the MSC 116 performs its functions whiletaking into account mobility management aspects of the subscriber,including authentication, ciphering, radio resource management, andlocation register updating procedures. The MSC 116 also allows thewireless access communication unit 106 interworking to the PSTN 125. TheMSC 116 may be part of a digital multiplex system (DMS) “super-node”based switching system, capable of providing the switching functions ina cellular network. Also, the visitor location register (VLR) ispreferably co-located and integrated with the MSC 116.

The MSC 116 may support a variety of interfaces. The MSC 116 may supportan A-interface providing linkage between the MSC 116 and the basestation subsystem (BSS), particularly the base station controller 112and the transcoding unit 115, and a PSTN interface which is used forconnecting the MSC 116 to the PSTN 125 across which voice and circuittraffic is transmitted. The MSC 116 also may support a mobileapplication part (MAP) interface, which is a CCS7 application permittingmobility information to be transferred among network level components.In addition, the MSC 116 may support a billing center interface, whichis used for connecting the MSC 116 to a downstream processor fordownloading of billing events; an operations management center (OMC)interface, which is used to administer the MSC 116 and visitor locationregister (VLR); and a service center interface, which is used forconnecting the service center function responsible for relaying andstore-and-forwarding short messages to mobile stations.

A variety of functions are preferably performed by the MSC 116. Forexample, the MSC 116 preferably authenticates subscribers and, ifaccessible to the system, mobile stations. The MSC 116 interfaces to thePSTN 125, and may interface to, for instance, public land mobilenetworks (PLMNs) or PCS-1900 networks. The MSC 116 also providesterrestrial channel allocation, and call control and signaling support.In addition, the MSC 116 may perform echo cancellation towards the PSTN125, handling and management of database information, charge recording,handling of subscriber registration and location management, andoperation measurements.

The MSC 116 is connected to a home location register (HLR) andauthentication center (AuC), collectively shown as an integrated unitHLR/AuC 123 in FIG. 1. The HLR/AuC 123 may be built on a digital (e.g.,DMS) super-node platform, and interconnect with various functionalentities including the visitor location register, MSC, and mobileapplication part (MAP). The HLR component of the HLR/AuC 123 containsinformation about subscribers, services assigned to the subscribers, thestatus of such services, and any further information required to supportthe operation of the services when active. The HLR responds to requestsfrom the MSC 116 and/or VLR to provide or update subscriber data. TheHLR communicates with the VLR to download subscriber data and to obtaincall routing information for the mobile stations in the region coveredby the VLR.

The AuC component of the HLR/AuC 123 contains subscriber keys for use inauthenticating attempts to access the network. The AuC component usessubscriber keys to generate authentication vectors, as further describedherein, which are provided to the VLR via the HLR component.

In a mobile system, such as a PCS 1900 mobile system, the informationheld by the HLR component of the HLR/AuC 123 allows mobile stations tobe addressed by means of a unique number, regardless of geographiclocation, thus allowing mobile stations to roam freely within andbetween networks. In a system providing fixed access wireless servicesin which a wireless access communication unit 106 and related componentsare utilized, the HLR component contains information similar to thatmaintained for mobile stations in a completely mobile-based system. TheHLR component of the HLR/AuC 123 contains information regarding thesubscribers interfacing with the wireless access communication unit 106.As noted previously, the individual CPE trunks connected to the wirelessaccess communication unit 106 (such as CPE trunks 602 shown in FIG. 6)may appear as individual subscribers (i.e., “mobile stations”) to theHLR and VLR. Hence, each CPE trunk connected to the wireless accesscommunication unit 106 has its own (preferably unique) subscriberidentity number. The subscriber identity number may, as notedpreviously, comprise an international mobile subscriber identity (IMSI),which is a unique, permanent identifier of a CPE trunk assigned at thetime of manufacture of the CPE 105, or may comprise a mobile subscriberISDN (MSISDN) number, which would be one of the public PSTN numbersassigned to the CPE 105.

Because the wireless network is likely to be configured to serviceindividual mobile subscribers as well as being capable of servicing thewireless access communication until 106, the wireless accesscommunication until 106 may include functionality for keeping itsnon-mobile aspects transparent from the wireless network. For example, amobile telephone subscriber may occasionally signal the wireless networkto refresh the VLR on a regular basis. To keep the fixed wirelessaspects of the system transparent to the wireless network, the wirelessaccess communication unit 106 may periodically perform network-levelregistration using, for example, a GSM periodic registration mechanism,to keep the VLR entries for the “subscribers” alive. The wireless accesscommunication until 106 may also perform network-level registrationevery time it registers through a base station 109 in a location areadifferent from that of the base station 109 to which it was previouslyconnected. Further details regarding initial and periodic registrationmay be found in e.g., copending U.S. application Ser. No. 08/987,872filed concurrently herewith, and previously incorporated herein byreference.

Certain features relating to voice call establishment and maintenancewill now be described in more detail, with reference to the interactionamong various components of a communication system in which the wirelessaccess communication unit 106 is deployed.

For “outgoing” voice call establishment initiated by the CPE 105 thewireless access communication unit 106 handles acquisition of anover-the-air communication channel, mobility management connectivity,and call setup, and in addition is preferably capable of handlingvarious error or exception conditions. When the wireless accesscommunication unit 106 detects a trunk seizure by the CPE 105, thewireless access communication unit 106 marks the CPE trunk as “busy” andissues a dial tone (assuming that it is able to communicate with a basestation 109). In parallel, the wireless access communication unitinitiates an over-the-air communication channel acquisition procedure.The dial tone is removed when the wireless access communication unit 106detects the first dialed digit from the CPE 105, or if it detects anon-hook from the CPE 105 prior to receiving any digits therefrom.

To facilitate initial acquisition of over-the-air communicationchannels, upon initial power-up the wireless access communication unit106 preferably performs a thorough search of nearby base stations 109 tofind a suitable base station 109. The wireless access communication unit106 establishes communication with the base station 109, and receives asurrounding base station map from the current base station 109. Thesurrounding base station map provides the wireless access communicationunit 106 with a list of neighboring base stations 109 that arecandidates for over-the-air communication. Using the surrounding basestation map, the wireless access communication unit 106 builds up a basestation selection table containing such things as signal qualityinformation on the neighboring base stations 109. The base stationselection table is stored in non-volatile memory in the wireless accesscommunication unit 106. On subsequent power-ons, the wireless accesscommunication unit 106 uses the existing base station selection table tospeed up its base station acquisition.

On receiving a trigger from the CPE 105 to set up an outgoing call orperform a registration, the wireless access communication unit 106attempts to acquire an over-the-air communication channel. In certainwireless systems the acquisition of an over-the-air communicationchannel is accomplished by interacting with a control channel of thewireless system. In certain types of TDMA systems, the channelacquisition process may entail acquiring a time slot in a time frameestablished by the base station 109. Acquisition of a time slot may becarried out, for example, according to a handshake protocol described inmore detail in U.S. Pat. No. 5,455,822, assigned to the assignee of thepresent invention, and hereby incorporated by reference as if set forthfully herein.

In another aspect of the invention, each CPE trunk supported by thewireless access communication unit 106 represents a logical subscriberto the network, even though the multiple CPE trunks are physicallyconnected to the wireless access communication unit 106. Thus, forexample, where four CPE trunks 602 are connected to the wireless accesscommunication unit 106, four unique subscriber identifiers areallocated. The use of different logical subscriber identifiers for eachCPE trunk 602 permits multiple calls to be handled by the wirelessaccess communication unit 106 across one or more wireless links to thebase station 109. In a particular embodiment, each CPE trunk isidentified with its own unique international mobile subscriber identity(IMSI) number and mobile station ISDN (MSISDN) number for addressing.When the wireless access communication unit 106 initiates “mobilitymanagement” and call control procedures on behalf of one of theconnected CPE trunks, it uses the IMSI assigned to that CPE trunk.

To the network side of the system (i.e., the base station 109, basestation controller 112, MSC 116, etc.), each logical subscriberassociated with the wireless access communication unit 106 is seen as aseparate user, much like the separate mobile subscribers that can alsocommunicate wirelessly with the base station 109. The base station 109generally need not know that a group of different IMSIs belongs to asingle entity (i.e. the wireless access communication unit 106). TheIMSIs are preferably held on one or more subscriber interface module(SIM) chips, programmed at the factory. Each SIM chip, once placed inthe wireless access communication unit 106, belongs to a specific CPEtrunk. The IMSI is used, as described elsewhere herein, for such thingsas registration, authentication. and network access.

For each IMSI stored in the wireless access communication unit 106 therepreferably is a corresponding MSISDN stored in the HLR component of theHLR/AuC 123. Tile MSISDN number may be the equivalent of the NANP numberconverted into an MSISDN number—i.e., a number in the format of1+NPA+NXX+XXXX. The MSISDN number is used for such things as callorigination and billing generation. The MSISDN number may be one of thepublic PSTN numbers assigned to the CPE 105; therefore, the MSISDNnumber may be assigned to the CPE 105 from the PSTN 125.

The wireless access communication unit 106 may be assigned anidentifying serial number in the form of an International MobileEquipment Identity (IMEI) number. The IMEI number may be assigned at thefactory, and each wireless access communication unit 106 is preferablyassociated with a unique IMEI number. If an Equipment Identity Register(EIR) element is used within the network, it will contain the IMEInumber of each wireless access communication unit 106 in the system.Alarms generated by the wireless access communication unit 106 may usethe IMEI number for identification purposes.

FIG. 10 is a diagram showing interfaces between different components ofa communication system 801 according to a preferred embodiment of thepresent invention. Some of these interfaces have been generallydescribed previously with respect to the preferred base station 501shown in FIG. 5. The different interfaces shown in FIG. 10 include anover-the-air interface or “O-interface” 560 between a wireless accesscommunication unit 106 and the base station 109, an internal interfaceor “I-interface” 561 internal to the base station 109 (i.e., between theOTA manager 502 and the line card manager 503 of the preferred basestation 501, as shown in FIG. 5), and a network interface or“N-interface” 562 between the base station 109 and the base stationcontroller 112. The base station controller 112 communicates with theMSC 116 over a standard interface such as the GSM A interface 571.

In a preferred embodiment, in accordance with the embodiment of theinvention shown in FIG. 1, a transcoding unit 115 is interposed betweenthe base station controller 112 and the MSC 116. In this embodiment, anadditional interface designated the “T-interface” is provided betweenthe base station controller 112 and the transcoding unit 115, and thetranscoding unit 115 communicates with the MSC 116 over a standardinterface such as the GSM A interface 571.

Aspects of some of the communication interfaces shown in FIG. 10 willnow be described in more detail, starting with the “O-interface” 560between the wireless access communication unit 106 and the base station109. The “O-interface” 560 comprises one or more wireless, over-the-aircommunication channels, each channel preferably (but not necessarily)including a forward communication link and a reverse communication linkto support full duplex communication. The over-the-air communicationchannel(s) of the O-interface 560 may be implemented according to any ofa variety of different multiple-access communication protocols,including protocols utilizing time division multiple access (TDMA),frequency division multiple access (FDMA), or code division multipleaccess (CDMA), or various combinations thereof. The O-interface 560 mayinclude, in some alternative embodiments, wireless broadcast channelsfrom the base station 109 that are used, for example, for transmittingcontrol traffic and signaling information. In other embodimentsdedicated broadcast control channels are not used.

One possible communication protocol that may be used for communicatingacross the O-interface 560 in one embodiment of the present invention isdepicted in FIG. 16. The protocol depicted in FIG. 16 makes use of timedivision multiple access (TDMA) and spread spectrum techniques. As shownin FIG. 16, a polling loop 1380 (“major frame”) comprises a plurality oftime slots 1381 (“minor frames”). Each minor frame 1381 comprisescommunication between a base station 109 (e.g., cellular station) and auser station (e.g., mobile user) in time division duplex—that is, thebase station 109 transmits to a user station and the user stationtransmits back to the base station 109 within the same minor frame 1381.

Another communication protocol that may be used for communication acrossthe O-interface 560 is depicted in FIG. 17. The protocol depicted inFIG. 17 uses aspects of both FDMA (in the sense that transmissions aredistinguished by different frequency allocations) and TDMA (in the sensethat transmissions are distinguished by separate time allocations). Asshown in FIG. 17, one frequency band 1510 is allocated to a base station109 for base-to-user transmissions, and another frequency band 1511 isallocated to user stations (e.g., handsets, or other wireless units) foruser-to-base transmissions. A repeating major time frame (or “pollingloop”) 1501 is defined for communication over each frequency band 1510,1511. A plurality (e.g., sixteen) of base time slots 1502 and user timeslots 1503 are defined within the repeating major time frame 1501, withthe user time slots 1503 preferably lagging behind the base time slots1502 by an amount of time. In a preferred embodiment, in which sixteenbase time slots 1502 and sixteen user time slots 1503 are defined ineach major time frame 1501, the time lag 1505 between the first basetime slot 1502 and first user time slot 1503 is a preset amount of timecorresponding to a number of time slots, such as eight time slots, andis therefore referred to as a “slot offset.” This time lag or slotoffset 1505 allows user stations time to receive transmissions over thebase frequency band 1510 in the assigned base time slot 1502, processthe base-to-user transmissions, perform a transmit/receive frequencyswitch, and transmit a reverse link transmission in the correspondinguser time slot 1503, without having to wait an entire time frameduration to transmit a reverse link transmission. The slot offset 1505can comprise an amount of time other than eight time slots, or the majortime frame 1501 can be defined such that there is no slot offset 1505 atall.

In one aspect of a preferred communication protocol, a single base timeslot 1502 and a single user time slot 1503 collectively comprise aduplex communication channel. In a preferred embodiment, the time frame1501 of the protocol described with reference to FIG. 17 supportssixteen base time slots 1502 and sixteen corresponding user time slots1503, for a total of sixteen possible duplex communication channels. Ina preferred embodiment, each base time slot 1502 and user time slot 1503is 1.35 milliseconds in duration, and each time slot permits 9.6kilobits/second for the transmission of encoded speech or other data.

Communication channels are preferably assigned to the wireless accesscommunication unit 106 on a demand basis, although they may, in certainembodiments, be pre-allocated as well. An advantage of dynamicassignment of over-the-air communication channels is that more users canbe supported. For the protocol shown in FIG. 17, over-the-aircommunication channels are preferably assigned based on requests fromthe wireless access communication unit 106 to the base station 109. Theassignment of over-the-air communication channels is carried out in thesame fashion for mobile users (if any) that also communicate with thebase station 109—i.e., according to the cellular communication protocolfor the network of which the base station 109 is a part. For example,over-the-air communication channels may be assigned with the assistanceof a dedicated control channel. Over-the-air communication channels mayalso be assigned according to techniques similar to those described in,for example. U.S. patent application Ser. No. 08/463,220 filed on Jun.5, 1995, hereby incorporated by reference as if set forth fully herein.Any other suitable mechanism for allocating or assigning over-the-aircommunication channels may also be used.

Details of a preferred I-interface 561 may be found in, e.g., U.S.patent application Ser. No. 08/610,193 filed on Mar. 4, 1996, herebyincorporated by reference as if set forth fully herein. Further detailsof the I-interface are also discussed herein with respect to FIG. 5.

The N-interface 562 connects the base station 109 to the base stationcontroller 112. and comprises both traffic and signaling communicationchannels. At the physical layer, the N-interface 562 uses a fractionalT1 service as the transport mechanism. Each fractional T1 link supportstransfer rates from 64 kilobits/second up to 1.536 megabits/second. Eachtime slot on the T1 link supports up to four 16 kilobit/second bearerchannels.

The traffic channels of the N-interface 562 include non-aggregated 16kilobit/second channels for carrying data (e.g., speech data) for oneradio traffic channel (i.e., one over-the-air communication channel). Upto four such traffic channels can be multiplexed into one 64kilobits/second T1 time slot. A single signaling channel is provided foreach base station 109 for carrying signaling and OAM&P information, at arate of 64 kilobits/second. The signaling traffic includes controlinformation pertaining to the link between the base station 109 and thebase station controller 112, as well as signaling traffic relayedbetween the wireless access communication unit 106 and the MSC 116.

FIG. 7 shows in more detail the interface signaling structures for theN-interface 562 used in conjunction with a preferred embodiment of theinvention. As shown in FIG. 7, a base station controller (BSC) 702 isconnected to a base station (OBTS) 703 over a plurality of logical links711 through 715, all of which are, from a physical standpoint,multiplexed onto a single digital timeslot channel (or DS0) andtransmitted using pulse code modulation (PCM). The base station 703shown in FIG. 7 comprises two transceivers 706, 707 (designated “TRX1”and TRX2,” respectively), which are identified by terminal endpointidentifiers TEI B and TEI C, respectively, and a base common function(BCF) 705, which is identified by terminal endpoint identifier TEI A.

Signaling messages for traffic control are transmitted on two of thelogical links 713 and 715, one of each connected to transceivers 706 and707. Signaling messages carried by logical links 713 and 715 forinteractions between the base station 703 and base station controller702 relate to functions such as, for example, backhaul and radioresource management, and mobility management. Signaling messages carriedby channels 713 and 715 also relate to end-to-end call control andmobility management signaling between the wireless access communicationunit 106 and the MSC 116, and are encapsulated Pithily transport notes.In addition, observation counters and operation measurements sent by thebase station 703 to the base station controller 702, and encapsulatedwithin transport notes, can be conveyed across logical links 713 and715.

Messaging related to management functions (such as OAM&P) is carried onlogical links 711, 712 and 714, to the base common function 705 andtransceivers 706 and 707, respectively. The OAM&P messaging provides formanagement of the base station 703 by the base station controller 703.

In a preferred embodiment, the base station controller 112 is connectedto a transcoding unit 115 over a T-interface, which is shown in FIG. 1but not explicitly shown in FIG. 10. The T-interface links the basestation controller 112 to the transcoding unit 115 over a T1 connection,which carries a variety of different links, including bearer voicechannel links and signaling links. The T-interface carries a pluralityof 16 kilobits/second bearer voice channels containing coded, encryptedvoice and FEC information, along with inband signaling informationbetween the base station 109 and the transcoding unit 115 (i.e., theendpoints of the encryption/decryption algorithms). In one embodiment,up to four such bearer voice channels can be multiplexed onto one DS0timeslot. The bearer voice channels are processed for transcoding andrate adaptation functionality by the transcoding unit 115, which formatsthe bearer voice channel data into 64 kilobits/second pulse-codemodulated (PCM) voice data for relay to the MSC 116.

In addition to bearer data, the T-interface also carries one or moresignaling links. For example, the T-interface carries signaling linksfor OAM&P control of the transcoding unit 115 by the base stationcontroller 112, using a standard LAPD data link The T-interface alsocarries SS7 signaling links between the base station controller 112 andthe MSC 116, each using one T1 DS0 timeslot. The signaling informationon these links is relayed transparently between the base stationcontroller 112 and the MSC 116 through the transcoding unit 115. TheT-interface may also optionally carry the communication link between thebase station 109 and the operations management center (OMC) 120.

The transcoding unit 115 (if provided) is connected to the MSC 116 overa standard interface such as the GSM A-interface. Alternatively, thefunctionality of the transcoding unit 115 may be incorporated in thebase station controller 112, which then would connect to the MSC 116over a standard interface such as the GSM A-interface. The A-interfaceis depicted in FIG. 1, and is also denoted in FIG. 7 by referencenumeral 571. Details of the GSM A-interface are described in, forexample, “Mobile Switching Center (MSC) to Base Station Subsystem (BSS)Interface; Layer 3 Specification,” GSM Recommendation 08.08. Preferably,some modifications are made to the standard GSM A-interface to supportthe features and functionality of the preferred embodiment orembodiments described herein. Such modifications may include, forexample, using a T1 line as the physical interface to carry both trafficand signaling, and using μ-law coding in certain geographical regions(such as North America).

Signaling links for the A-interface, in general, logically run betweenthe base station controller 112 and the MSC 116, whereas the bearerlinks span between the transcoding unit 115 and the MSC 116. Thetranscoding unit 115, as noted, processes the 16 kilobits/second bearerlinks received over the T-interface, and generates 64 kilobits/secondpulse-code modulation links towards the MSC 116. The A-interfacesignaling channels carry signaling connection control part (SCCP)logical signaling links. An SCCP link is maintained between the basestation controller 112 and the MSC 116 for each active CPE trunk (or“logical mobile station”) of the wireless access communication unit 106that is communicating with the PSTN 125. Signaling information carriedover the A-interface includes SS7 signaling between the base stationcontroller 112 and the MSC 116 for management of the link, A-interfaceradio resource management signaling, A-interface mobility managementsignaling, call control signaling, between the wireless accesscommunication unit 106 and the MSC 116 relayed through the base stationcontroller 112, and, optionally OAM&P signaling between the base stationcontroller 112 and the OMC 120. The A-interface signaling traffic passesthrough the transcoding unit 115 (if provided), and the transcoding unit115, as noted, relays the signaling information transparently betweenthe base station controller 112 and the MSC 116.

FIG. 8 is a diagram showing a protocol architecture for one particularembodiment of the preferred communication system 101, and furtherdepicts a preferred relationship of connections among the wirelessaccess communication unit 106, base station 109, base station controller112, and MSC 116 across the O-interface 560, N-interface 562 andA-interface 571. In the protocol architecture shown in FIG. 8, “CM”relates to connection management, “MM” relates to mobility management,“OTA” relates to the over-the-air protocol, “LAPD” relates to linkaccess protocol for the D channel, “IWF” relates to an interworkingfunction, “Ph L” relates to the physical layer, “BSSMAP” relates to thebase station subsystem management application part, “SCCP” relates toSS7 signaling connection control part, “MTP” relates to message transferpart (MTP Layers 2 and 3), “OAM” relates to operations, maintenance andadministration, “NTS-MM” relates to N-Notes mobility management, and“NTS-RR” relates to N-Notes radio resource management.

The call control protocol is the GSM direction transfer application part(DTAP) call control entity, shown as the GSM-CM layer in FIG. 8. ThisGSM DTAP call control entity (i.e., GSM-CM layer) supports a variety offeatures, including (1) the establishment, maintenance and release ofnormal outgoing voice calls (i.e., originating from the CPE 105) betweenthe wireless access communication unit 106 and the MSC 116; (2) theestablishment, maintenance and release of emergency (i.e., “911”)outgoing voice calls between the wireless access communication unit 106and the MSC 116; and (3) the signaling of DTMF tones from the CPE 105 inthe network direction during active calls. Preferably, transparent digittransmission is provided between the wireless access communication unit106 and the base station 109, since digit analysis is preferably carriedout at the base station 109. Further, the system also preferablyprovides transport capability via control transfer (CT-TRA) O-Notes forDTAP protocol messages.

A GSM DTAP mobility management entity, shown as the GSM-MM layer in FIG.8, is used end-to-end (between the wireless access communication unit106 and the MSC 116) to run various mobility management procedures,including authentication and subscriber identification. Other mobilitymanagement procedures are supported on the O-interface 560 and theN-interface 562 as part of the protocols utilizing O-Notes and N-Notes,and are shown as the OTA-MM entity and NTS-MM entity in FIG. 8.

The GSM-CM and GSM-MM protocol runs end-to-end between the wirelessaccess communication unlit 106 and the MSC 116, and the protocolmessages are relayed transparently through the base station 109 and thebase station controller 112. The protocol messages may be encapsulatedwithin transport O-Notes (CT-TRA) messages across the O-interface 560,transport N-Notes messages across the N-interface 562 using the LAPDsignaling link between the base station 109 and base station controller112, and BSSMAP messages over the A-interface 571 using the SCCPsignaling link.

The over-the-air mobility management procedures are interworked in thebase station 109 with N-Notes mobility management procedures, shown asthe NTS-MM Layer in FIG. 8. The NTS-MM procedures run over the LAPDsignaling link of the N-interface 562, and are interworked in the basestation controller 112 with corresponding DTAP mobility management(GSM-MM) procedures on the A-interface 571. The GSM-MM protocoltherefore runs partly end-to-end between the wireless accesscommunication unit 106 and the MSC 116, and partly between the basestation controller 112 and the MSC 116.

Over-the-air radio resource management functions are provided by an OTAradio resource (OTA-RR) management protocol entity shown in FIG. 8. Suchradio resource management functions include link acquisition, lost linkrecovery, bearer message ciphering, over-the-air slot negotiation andtime slot interchange (in a TDMA system), digit transmission andanalysis, assignment and mode change, link release (whether initiated bythe network or wireless access communication unit 106), base assistinformation, and surrounding base table information. On the O-interface560, the radio resource management is carried out as part of the O-Notesprotocol by the OTA-RR entity.

Over the N-interface 562, the NTS-RR protocol procedures for radioresource management include ciphering, assignment and mode change, andlink release. In addition to radio resource functions, the functionalityof the NTS-RR entity includes procedures to manage the allocation andde-allocation of bearer channels on the backhaul link(s) of theN-interface 562.

Various BSSMAP procedures are provided on the A-interface 571 forsupporting the functionality of the wireless access communication unit106. These BSSMAP procedures include, for example, assignment, blocking,reset, release, cipher mode control, and initial message.

Mobility management connection establishment for normal calls isinitiated by the mobility management entity (i.e., GSM-MM entity shownin FIG. 8) of the wireless access communication unit 106. To do so, themobility management entity sends a Connection Management (CM) ServiceRequest message to the MSC 116, with the Service Type field indicating anormal call. The MSC 116 responds by sending a CM Service Acceptmessage. Upon receiving a CM Service Accept message from the MSC 116,the wireless access communication unit 106 continues with normal callset-up, as further described herein and/or in related applicationsincorporated by reference elsewhere herein.

For normal calls, the mobility management connection establishmentprocedure may encompass an authentication procedure. Such a proceduremay be based on the DTAP mobility management signaling forauthentication, and may run end-to-end between the MSC 116 and thewireless access communication unit 106.

For emergency (i.e., “911”) calls, the mobility management entity (i.e.,GSM-MM entity shown in FIG. 8) of the wireless access communication unit106 initiates a mobility management connection establishment procedureby sending a CM Service Request message, with the CM Service Type fieldindicating an emergency call to the MSC 116. In response. the MSC 116transmits a CM Service Accept message to the wireless accesscommunication unit 106. Upon receiving the CM Service Accept messagefrom the MSC 116, the wireless access communication unit 106 continueswith emergency call setup. For emergency calls, the network need notinvoke an authentication procedure.

If the service request is rejected by the MSC 116, or if a servicerequest time-out expires, the wireless access communication unit 106 mayissue a reorder tone to the CPE 105. and abort the call establishmentprocedure.

Although the wireless access communication unit 106 preferably utilizesa mobility management connection establishment procedure in theestablishment of a call connection, the CPE trunks typically do notconstitute mobile components of the system. The communication system 101adapts techniques utilized in a mobile communication system forfacilitating setup and maintenance of a wireless trunk 108 through thewireless access communication unit 106, as generally described herein.Using aspects of a mobile communication system in the communicationsystem 101 which includes the wireless access communication unit 106 hasthe advantage of allowing existing mobile communication systeminfrastructures to support a wireless trunk in accordance with thepresent invention, without requiring a separate base station subsystemor other dedicated wireless path to the PSTN 125 to be constructed.

After the mobility management connection establishment procedure hasbeen completed, the wireless access communication unit 106 exchangesDTAP signaling with the MSC 116 to set up an outgoing call. The primarydifference between normal and emergency call setup procedures is in theway the call is initiated. For a normal call, the wireless accesscommunication unit 106 sends a DTAP Setup message to the base station109 with the Called Address field empty. The base station 109 fills inthe Called Address field of the Setup message with the digits storedearlier as part of the digit analysis procedure, before relaying theSetup message to the MSC 116 across the base station controller 112. Foran emergency call, the wireless access communication unit 106 sends aDTAP Emergency Setup message to the MSC 116. The DTAP Emergency Setupmessage is relayed transparently through the base station 109 and thebase station controller 112. The MSC 116 returns a DTAP Call Proceedingmessage to indicate acceptance of the call request.

Further aspects of the invention relate to security features of apreferred communication system 101 including the wireless accesscommunication unit 106. Such security features include, for example,authentication and ciphering.

Because the wireless access communication unit 106 may make use ofwireless resources of a nearby mobile cellular system, a possibilityexists that outside parties may attempt to make illegal use of theidentity of the wireless access communication unit 106 in the samemanner that such parties attempt to make illegal use of mobile handsets.For example, in many analog mobile telephone networks mobile telephonescan be cloned, causing large amounts of revenue to be lost due toillegal use of such telephones.

The preferred communication system 101 preferably uses an authenticationprocedure to prevent unauthorized use of network resources, and toprotect the wireless access communication unit 106 (and other wirelessentities) from fraudulent impersonations. Authentication is preferablyperformed with each user registration, as well as part of normal callsetup on a 1-in-N basis—i.e., once every N calls authentication isperformed, with N being configurable within the system.

In a preferred embodiment, authentication requests and responses arepassed between the MSC 116 and the wireless access communication unit106 as part of the GSM mobility management (MM) protocol, and are basedon the GSM A3/A8 authentication mechanism. At the user end, the wirelessaccess communication unit 106 contains a standard GSM SIM function foreach CPE trunk. A subscriber identity (i.e., IMSI) and subscriber keyvalue (K_(i)) are stored in the wireless access communication unit 106for each CPE trunk, within the GSM SIM function associated with the CPEtrunk. At the network end, the MSC 116 requests an authenticationinformation set from the home location register (HLR) component of theHLR/AuC 123. In a preferred embodiment, the authentication informationset comprises a set of three authentication parameters referred toherein as an authentication triplet. The HLR component of the HLR/AuC123 stores authentication information sets (previously requested andtransferred from the AuC component of the HLR/AuC 123) from which it mayselect the authentication triplet requested by the MSC 116, or it mayrequest a new authentication triplet from the AuC component of theHLR/AuC 123 and transfer the new set to the MSC 116.

An authentication triplet comprises a generated random number (RAND), asigned response (SRES) used for the authentication of a subscriber's SIMcard, and a ciphering key (K_(c)) used to encrypt and decryptinformation across the radio link between the wireless accesscommunication unit 106 and the network. The subscriber key value K_(i)stored at both the AuC component of the HLR/AuC 123 and at the wirelessaccess communication unit 106 is used in either two separate algorithms(generally known in the art as A3 and A8) or in a combined A3/A8algorithm which generates the ciphering key K_(c) and the signedresponse SRES for authentication procedures. A random number generatoris used at the AuC component of the HLR/AuC 123 to generate the randomnumber RAND, which is sent by the MSC 116 to the wireless accesscommunication unit 106. The wireless access communication unit 106 feedsthe random number RAND along with the subscriber key value K_(i) intothe A3 algorithm to generate the signed response SRES, and into the A8algorithm to generate the ciphering key K_(c).

The signed response SRES is returned to the MSC 116 and is subsequentlycompared by the visitor location register (VLR) with the signed responsevalue in the VLR. If the returned signed response SRES matches thesigned response value in the VLR, the subscriber is authorized toregister, make calls, and carry out other network interactions. If, onthe other hand, the returned signed response SRES does not match thesigned response value in the VLR, then the subscriber is blocked fromregistering, making calls, and carrying out other network interactions.In such a case, the base station 109 is informed by the MSC 116 that theauthentication attempt resulted in a failure, and the base station 109terminates the call connection to the wireless access communication unit106 with an authentication failure message.

Preferably, the AuC component of the HLR/AuC 123 and the SIM componentsare the only parts of the network which know about the existence of asubscriber key value K_(l) and the A3/A8 algorithm(s). The AuC componentof the HLR/AuC 123 generates a new random number RAND for eachauthentication request, and derives the signed response SRES andciphering key K_(c) which are then passed to the HLR component of theHLR/AuC 123 and MSC 116 as needed. The MSC 116 need not be involved inthe actual derivation of the signed response SRES or the ciphering keyK_(c).

FIG. 18 is a diagram illustrating authentication procedures, includingdivision of functionality, in a preferred embodiment of thecommunication system 101. As shown in FIG. 18, an authentication tripletincluding a random number RAND, signed response SRES, and ciphering keyK_(c) are stored in the VLR of the MSC 116, after being transferred uponrequest from the HLR/AuC 123. The random number RAND is sent to thewireless access communication unit 106, whereupon it is applied alongwith the subscriber key value K_(l) to locally generate the signedresponse SRES and ciphering key K_(c). The signed response SRES isreturned by the wireless access communication unit 106 to the MSC 116for comparison against the SRES stored at the VLR of the MSC 116. Theciphering key K_(c) is used thereafter for ciphering transmissionsacross the wireless communication channel.

Bearer ciphering at the user end is performed at the wireless accesscommunication unit 106. Ciphering of bearer information on the networkend is preferably carried out at the transcoding unit 115. Ciphering ofsignaling messages (e.g., control traffic) may optionally be carriedout. A wide variety of suitable algorithms may be selected for bearerciphering. For example, the GSM A5/1 algorithm may be utilized for sucha purpose.

As part of call establishment, ciphering may be set up using a ciphermode setting procedure in conjunction with establishment of theciphering key K_(c) during the authentication process. The ciphering keyK_(c) may be relayed from the MSC 116 to the base station controller112, which in turn relays it to the base station 109 using signalingmessages across the N-interface 562. The base station 109 in turn relaysthe ciphering key K_(c) back to the transcoding unit 115, using inbandsignaling.

Further details regarding registration, de-registration and call setupwill now be described. FIG. 17 is a call flow diagram illustrating anetwork-level registration procedure. As a first step in the procedureillustrated in FIG. 12, the wireless access communication unit 106acquires a wireless communication channel (e.g., a time slot in a TDMAor TDD system, or a frequency channel in an FDD system, or other definedchannel) to a nearby base station 109. The wireless communicationchannel is acquired according to the particular protocol utilized by thewireless system. The wireless access communication unit 106 thenperforms a network-level registration procedure, according to theparticular registration protocol utilized by the system. Theregistration procedure may involve, for example, a location updatingprocedure on the A-interface. The wireless access communication unit 106performs network-level registration at regular intervals thereafter,with periodicity controlled by the network infrastructure. The wirelessaccess communication unit 106 may also perform network-levelregistration if it starts communicating through a base station 109 in adifferent location area from the base station with which it had beenpreviously communicating. After registration, the wireless communicationchannel is surrendered, and the MSC 116 initiates a resource releaseprocedure, as illustrated in FIG. 12.

In addition to network-level registration, the wireless accesscommunication unit 106 may also perform periodic registration with thebase station 109 at regular intervals, with a periodicity controlled bythe base station 109. For each registration attempt, the wireless accesscommunication unit 106 acquires a wireless communication channel,registers, and then surrenders the wireless communication channel,unless a call is in progress. If a call is in progress, the wirelesscommunication unit 106 need not acquire a new channel, but can, ifpossible under the particular wireless protocol, send registrationinformation over the existing communication channel. In addition toperiodic base-level registration, the wireless access communication unit106 also performs initial registration with a base station 109 when itstarts communicating through a base station different from but in thesame location area as a base station with which it was previouslycommunicating.

De-registration is performed by the system on behalf of each CPE trunkconnected to the wireless access communication unit 106 when thewireless access communication unit 106 is powered off. FIG. 13 is a callflow diagram illustrating a network level de-registration procedure. Asa first step in the procedure illustrated in FIG. 13, the wirelessaccess communication unit 106 acquires a wireless communication channel(e.g., a TDMA time slot) to a nearby base station 109. The wirelesscommunication channel is acquired according to the particular RFprotocol utilized by the wireless system. The wireless accesscommunication unit 106 then performs a network-level de-registrationprocedure, such as an IMSI detach procedure, according to the particularprotocol utilized by the system. After de-registration, the wirelesscommunication channel is surrendered, and the MSC 116 initiates aresource release procedure, as illustrated in FIG. 13.

After registration by the wireless access communication unit 106,outgoing calls ma be placed to the PSTN 125 via the CPE 105, wirelessaccess communication unit 106 and base station subsystem. This willgenerally involve provision of a dial tone, digit transmission, digitanalysis and call setup for outgoing calls under various types of CPEembodiments, including PBXs and KTSs with different levels of routingintelligence. These procedures are described in more detail in thecopending applications previously incorporated herein by reference.

FIGS. 14 and 15 are call flow diagrams illustrating successful callsetup procedures in two scenarios. FIG. 14 illustrates a call flow for asuccessful CPE-originated normal (i.e., non-emergency) call setupsequence, with non-PSTN interworking at the MSC 116. As depicted in FIG.14, provision of the dial tone, transmission of digits and digitanalysis is carried out according to techniques described in thecopending applications previously incorporated herein by reference. Ineach instance the call flow terminates with an end of dialing indicationfrom the base station 109 to the wireless access communication unit 106.Upon receiving the end of dialing indication from the base station 109,the wireless access communication unit 106 initiates a mobilitymanagement connection establishment procedure for a normal call. Thisprocedure results in an SCCP link being established for the call acrossthe A-interface 571 (assuming a GSM system), and further results in amobility management connection being set up with the MSC 116 forhandling the call. Part of this procedure may, if desired, entailauthentication and cipher mode setting procedures for the call.

After completion of the mobility management connection procedure, thewireless access communication unit 106 sends a direct transferapplication part (DTAP) Setup message to the base station 109, asillustrated in FIG. 14. The DTAP Setup message contains an empty calledparty address field, and is directed towards the MSC 116. The basestation 109 intercepts the DTAP Setup message and fills in the calledaddress field with the digits received from the wireless accesscommunication unit earlier during the digit analysis step. The basestation 109 then forwards the DTAP Setup message, via the base stationcontroller 112, to the MSC 116. The MSC 116 acknowledges the receipt ofthe DTAP Setup message by sending a DTAP Call Proceeding message to thewireless access communication unit 106, as illustrated in FIG. 14.

A bearer resource assignment procedure is then executed on eachinterface of the wireless fixed-access system, starting from theA-interface 571 and progressing to the O-interface 560. The bearerresource assignment procedure results in bearer channels being assignedon the A-interface 571, N-interface 562 and O-interface 560, and aswitched connection being set up through the base station controller112.

After the bearer resource assignment procedure is complete, the MSC 116sends a DTAP Alerting message to the wireless access communication unit106. The wireless access communication unit 106 provides a ringback toneto the user 102, via the inband path through the CPE 105 (i.e., the PBXor KTS, or other similar system). When the called party answers thecall, the MSC 116 sends a DTAP Connect message to the wireless accesscommunication unit 106. At that point the wireless access communicationunit 106 attaches its speech path and removes the ringback tone to theuser 102. The wireless access communication unit 106 responds to the MSC116 with a DTAP Connect Acknowledgment message, and the call is then ina conversation state.

FIG. 15, like FIG. 14, illustrates a call flow for a successfulCPE-originated normal call setup sequence, but with PSTN interworking atthe MSC 116. As depicted in FIG. 15, provision of the dial tone,transmission of digits and digit analysis is carried out as describedwith respect to FIG. 14. Upon receiving an end of dialing indicationfrom the base station 109, the wireless access communication unit 106initiates a mobility management connection establishment procedure for anormal call. Similar to the call flow of FIG. 14, this procedure resultsin an SCCP link being established for the call across the A-interface(assuming a GSM system), and further results in a mobility managementconnection being set up with the MSC 116 for handling the call. Part ofthis procedure may, if desired, entail authentication and cipher modesetting procedures for the call.

After completion of the mobility management connection procedure, thewireless access communication unit 106 sends a DTAP Setup message to thebase station 109. The DTAP Setup message contains an empty called partyaddress field, and is directed towards the MSC 116. The base station 109intercepts the DTAP Setup message and fills in the called address fieldwith the digits received from the wireless access communication unitearlier during the digit analysis step. The base station 109 thenforwards the DTAP Setup message, via the base station controller 112, tothe MSC 116. The MSC 116 acknowledges the receipt of the DTAP Setupmessage by sending a DTAP Call Proceeding message to the wireless accesscommunication unit 106, as illustrated in FIG. 15. A bearer resourceassignment procedure is then executed on each interface of the wirelessfixed-access system, starting from the A-interface and progressing tothe O-interface, similar to the call flow of FIG. 14. The bearerresource assignment procedure results in bearer channels being assignedon the A-interface, N-interface and O-interface, and a switchedconnection being set up through the base station controller 112.

After the bearer resource assignment procedure is complete, the MSC 116sends a DTAP Progress message to the wireless access communication unit106, indicating interworking with the PSTN 125. The wireless accesscommunication unit 106 attaches its speech path at this point. Thenetwork senses the ringback tone over the connected speech path, and theringback tone is relayed by the wireless access communication unit 106to the user 102, via the CPE 105 (i.e., the KTS or PBX, or other similarsystem). When the called party answers the call, the network removes theringback tone. The MSC 116 sends a DTAP Connect message to the wirelessaccess communication unit 106. The wireless access communication unit106 responds with a DTAP Connect Acknowledgment message and the callthen moves to a conversation state.

In either call flow scenario depicted in FIG. 14 or 15, if the calledparty is busy, the call will generally be rejected. In the case ofnon-PSTN interworking, a busy tone is sent from the wireless accesscommunication unit 106 to the user 092 in response to a DTAP Disconnectmessage from the MSC 116, and a DTAP release procedure is initiated.When an on-hook signal is detected from the user 102, the wirelessaccess communication unit 106 initiates a call resource releaseprocedure. In the case of PSTN-interworking, the busy tone is sent fromthe PSTN 125. When the CPE 105 detects an on-hook signal from the user102, it sends a disconnect message to the wireless access communicationunit 106, which then initiates a DTAP release procedure followed by acall resource release procedure.

While one or more embodiments have been described above in accordancewith various aspects of the present invention, a number of variations ofthese embodiments exist incorporating the same or similar principles ofoperation as described herein. For example, it will be apparent to oneskilled in the art that the functionality of the CPE 105 and thewireless access communication unit 106 can be combined into a singleunit. Also, one or more telephone stations 102 can be connected directlyto the wireless access communication until 106, bypassing the CPE 105.Also, the CPE 105 need not be connected to the telephone stations 102with telephone lines, but may be wirelessly connected thereto (i.e., awireless PBX).

A local area communication system according to certain aspects of thepresent invention may be comparatively easy to deploy in remote and/orrural areas, in contrast to systems requiring landline connections froma PBX or KTS to the network. With the addition of connecting thewireless access communication unit to the PBX or KTS, a remotely-locatedlocal area communication system can obtain benefits of a wirelessnetwork (including long distance access) for relatively little extradeployment effort.

While preferred embodiments of the invention have been described herein,many variations are possible which remain within the concept and scopeof the invention. Such variations would become clear to one of ordinaryskill in the art after inspection of the specification and the drawings.The invention therefore is not to be restricted except within the spiritand scope of any appended claims.

1. A method comprising: connecting a wireless access communication unitto a plurality of non-wireless communication devices; establishing awireless connection between the wireless access communication unit and anetwork; transmitting a subscriber identifier from the wireless accesscommunication unit to the network over the wireless connection, thesubscriber identifier corresponding to one of a plurality of subscriberports of the wireless access communication unit; transferring, undersupervision of a controller, information between a radio unit of thewireless access communication unit and the plurality of subscriber portswhile the wireless access communication unit is wireless connected tothe network; receiving an authentication parameter from the network overthe wireless connection at the wireless access communication unit; andgenerating an authentication key at the wireless access communicationunit based upon the authentication parameter and a locally stored userkey value associated with the one of the plurality of subscriber portsof the wireless access communication unit.
 2. The method of claim 1,wherein the authentication key comprises a signed response, the methodfurther comprising transmitting the signed response from the wirelessaccess communication unit to the network over the wireless connection.3. The method of claim 1, wherein the authentication key comprises aciphering key, the method further comprising encrypting and decryptingmessages transmitted across the wireless connection using the cipheringkey.
 4. The method of claim 1, further comprising determining whether aconnection is to be established via the wireless access communicationunit or a public switched telephone network (PSTN).
 5. A wireless accesscommunication unit comprising: a plurality of subscriber ports toconnect to a customer premises telephone switch to establish a pluralityof communication paths between the wireless access communication unitand a plurality of non-wireless communication devices connected to thecustomer premises telephone switch; a plurality of subscriberinterfaces, each subscriber interface connected to one of the subscriberports; a radio transceiver to transmit and receive information over awireless connection to a base station; a controller connected to theradio transceiver and the subscriber interfaces, the controller tomanage transfer of ongoing call information between the radiotransceiver and the subscriber interfaces; and a subscriber identitymodule connected to one of the subscriber interfaces, the subscriberidentity module having a non-volatile memory to store a subscriberidentifier and a user key value, the subscriber identity module tooutput a signed response value in response to an authenticationparameter received by the radio transceiver over the wirelessconnection.
 6. The wireless access communication unit of claim 5,wherein the authentication parameter comprises a random numeric value.7. The wireless access communication unit of claim 5, wherein thesubscriber identity module is to output a ciphering key in response tothe authentication parameter.
 8. The wireless access communication unitof claim 5, wherein the controller is to utilize the ciphering key toencrypt and decrypt information transferred between the radiotransceiver and the one of the subscriber interfaces.